This is a 79mm (500cc) piston to fit Norton 79mm x 100mm Lonstroke singles - from well known piston manufacturer - JP Pistons. These pistons are CNC machined and very well made. The piston shown here is of the none-slipper type orignally fitted to ES2 and CS1 engines, and is almost identical to the original Hepolite construction. I have compared this piston back to back with an original ES2 piston, and the only difference I can see is that this piston looks to have a fractionaly higher piston crown, which I would estimate to be approximately 7:1 compression ratio. If you do not mind a slightly lower compression ratio than the normal International piston (i.e. approx 8.5:1) and you are not intending to use the engine for serious racing, then I would see no reason why this piston could not be used in SOHC Norton engines. I am able to supply this piston in STD, +0.020, +0.040 and +0.060 sizes. Note: When sizing pistons - the size represents the diameter of the bore, which means for a STD piston the bore should be exactly 79mm in diameter, and oversizes the exact number of thou on top of this (i.e.79mm + 0.020"). This listing is for a +0.040 (i.e. 79mm bore exactly) size piston